The present invention relates to a sheet transport apparatus that transports sheets.
For example, in electrophotographic image forming apparatuses, an electrostatic latent image is formed on the surface of a photosensitive drum; a toner image is formed on the surface of the photosensitive drum by developing the electrostatic latent image on the surface of the photosensitive drum using a developer; the toner image is transferred from the photosensitive drum to a sheet while the sheet sandwiched in a nip region between the photosensitive drum and a transfer member is being transported; and the sheet is heated and pressed, thereby fixing the toner image on the sheet.
In such image forming apparatuses, a sheet transport apparatus is incorporated, and the sheet is drawn out from a paper feeding tray and transported by such a sheet transport apparatus. In a transport path of the sheet transport apparatus, a registration roller (also called PS (Paper Stop) roller) is provided at an upstream side of the nip region between the photosensitive drum and the transfer member in the sheet transportation direction. The sheet is transported to the nip region by the registration roller after the leading edge of the sheet is put against the registration roller so as to flex the sheet so that the leading edge of the sheet is arranged in parallel to the registration roller due to the flexibility of the sheet. This prevents the sheet from obliquely passing through the nip region, avoiding obliquely transferring of the toner image onto the sheet.
Furthermore, in JP 2005-154100A (in the following, Patent Document 1), a guide member for sheets is biased by a spring at an upstream side of the registration roller in the sheet transportation direction, and the guide member effectively presses the leading edge of the sheet toward the registration roller, so that the leading edge of the sheet is reliably arranged by the registration roller.
Meanwhile, sheet blockage during transportation of the sheet, called a “jam”, may occur in sheet transport apparatuses. Thus, the apparatus is made so that a plurality of portions of the apparatus can be opened, and the blocked sheet can be removed at the opened portion.
However, when the portion provided with springs biasing the guide member for sheets as in Patent Document 1 is opened, it is possible that the user may touch the springs and, therefore, the springs may be removed or the spring itself may be damaged by careless operations and the like, causing failures in the apparatus.